JP5737557B2 - Stability evaluation method and stability evaluation apparatus - Google Patents

Description

  The present invention relates to a stability evaluation method and a stability evaluation apparatus for evaluating the stability of natural ground around a mine shaft.

  Conventionally, in the nuclear fuel cycle as shown in FIG. 14, how to dispose of high-level radioactive waste has been an important issue. As shown in FIG. 14, the high-level radioactive waste is a waste liquid with a high radioactivity level generated in the process of recycling spent fuel, which is solidified with glass. Since high-level radioactive waste maintains a high radioactivity level for a long period of time, it is required to be isolated and safely disposed of from the human living environment.

  In view of such a situation, as one of the disposal methods for high-level radioactive waste, a geological disposal in which a tunnel group is constructed deep underground and the high-level radioactive waste is buried in the tunnel group is being studied. . FIG. 15 is a diagram showing a schematic configuration of a geological disposal facility for high-level radioactive waste. The geological disposal facility includes a plurality of disposal tunnels (tunnels), a main tunnel that connects these disposal tunnels, and several types of shafts that connect the main tunnel to a ground receiving facility. In the case of Japan, it is stipulated by law that the geological disposal facility should be installed deeper than 300m underground.

  In the above-mentioned geological disposal facility, it is required to correctly evaluate the underground tunnel support and the stability of surrounding ground before construction. Of these, the most important is an evaluation method for the stability of natural ground around the tunnel. As a method for evaluating the stability of a conventional ground used in a tunnel, a method for evaluating the stability using an allowable wall strain is known (for example, see Patent Document 1).

JP 2009-114697 A

  However, the above-described prior art of Patent Document 1 has a problem in that the evaluation accuracy is low when applied to a case where the mine has a mine shape other than a circular shape or a complicated excavation.

  The present invention has been made in view of the above, and a stability evaluation method capable of maintaining high evaluation accuracy even when applied to a case where a tunnel shape other than a circular shape or a complicated excavation is performed, and An object is to provide a stability evaluation apparatus.

  In order to solve the above-described problems and achieve the object, the stability evaluation method according to the present invention is a stability evaluation method for evaluating the stability of a natural ground around a tunnel, and the geological condition of the natural ground and the tunnel The stress-strain curve obtained from the triaxial compression test of the natural ground material is assumed to be the value of the axial strain, assuming that the natural ground conforms to the Mohr-Coulomb yield criterion. By performing the numerical analysis of the excavation of the natural ground in the tunnel part based on the model forming process that forms the piecewise linear strain softening model that is divided and linearized in the model formation process, and the piecewise linear strain softening model formed in the model forming process, A numerical analysis step for calculating a nonlinear strain measure in a predetermined excavation section, a nonlinear strain measure calculated in the numerical analysis step, and a predetermined axis in the piecewise linear strain softening model And having a comparison step of evaluating the stability of the ground mountain by comparing the allowable value and a nonlinear distortion measure corresponding to Zumi.

  The stability evaluation method according to the present invention corresponds to the nonlinear strain measure when the nonlinear strain measure calculated in the numerical analysis step is equal to or less than the allowable value as a result of the comparison in the comparison step. The displacement calculation step for calculating the wall displacement to be performed, the excavation step for excavation according to the conditions set in the design step, the measurement step for measuring the wall displacement of the tunnel excavated in the excavation step, and the displacement calculation step And an evaluation step for evaluating the stability of the excavated ground based on the wall displacement measured and the wall displacement measured in the measurement step.

  In the stability evaluation method according to the present invention as set forth in the invention described above, the predetermined axial strain has a value equal to or greater than an elastic limit strain in the piecewise linear strain softening model.

  Further, the stability evaluation apparatus according to the present invention is a stability evaluation apparatus for evaluating the stability of a natural ground around a mine shaft, and includes a condition including a geological condition of the natural ground and an installation condition of the mine road, and the natural ground is According to the Mohr-Coulomb yield criterion, a piecewise linear strain softening model formed by dividing and linearizing the stress-strain curve obtained from the triaxial compression test of the natural ground material by the value of the axial strain. And a numerical analysis unit for calculating a nonlinear strain measure in a predetermined excavation section by performing numerical analysis of excavation of a natural ground based on a piecewise linear strain softening model stored in the storage unit. By comparing the nonlinear strain measure calculated by the numerical analysis unit with an allowable value which is a nonlinear strain measure corresponding to a predetermined axial strain, the stability of the natural ground is improved. A comparing unit worth, characterized by comprising a.

  Further, the stability evaluation apparatus according to the present invention corresponds to the nonlinear strain measure in the above invention, when the comparison unit compares the nonlinear strain measure calculated by the numerical analysis unit with the allowable value or less. The stability of the excavated ground is evaluated based on the displacement calculating unit that calculates the wall displacement to be performed, the wall displacement calculated by the displacement calculating unit, and the wall displacement measured in the tunnel excavated according to the conditions And an evaluation unit.

  In the stability evaluation apparatus according to the present invention as set forth in the invention described above, the predetermined axial strain has a value equal to or greater than an elastic limit strain in the piecewise linear strain softening model.

  According to the present invention, it is assumed that the natural ground conforms to the Mohr-Coulomb yield criterion, and that the piecewise linearization is performed by linearizing the stress-strain curve obtained from the triaxial compression test of the natural ground material by the value of the axial strain. Comparing the nonlinear strain measure calculated by forming a strain softening model and numerically analyzing the excavation of the ground in the tunnel based on this model, and the allowable value, which is a nonlinear strain measure corresponding to a given axial strain Thus, since the stability of the natural ground is evaluated, it is possible to maintain high evaluation accuracy even when it is applied to a case where a mine shape other than a circular shape or a complicated excavation is performed.

FIG. 1 is a block diagram showing a configuration of a stability evaluation apparatus according to an embodiment of the present invention. FIG. 2 is a diagram showing an outline of a piecewise linear strain softening model. FIG. 3 is a diagram showing a stress-strain curve obtained from a triaxial compression test. FIG. 4 is a diagram showing the relationship between elastic limit strain, peak strain, softening initiation strain, flow initiation strain and restraint pressure. FIG. 5 is a diagram showing the relationship between the state strain ratio and the restraint pressure. FIG. 6 is a diagram illustrating the relationship between axial differential stress and axial strain and the relationship between volumetric strain and axial strain in a piecewise linear strain softening model obtained by a triaxial compression test. FIG. 7 is a flowchart showing an outline of processing of the stability evaluation method according to the embodiment of the present invention. FIG. 8 is a diagram showing a setting example of the cross-sectional shape and dimensions of the mine shaft. FIG. 9 is a diagram schematically illustrating a setting example of a region to be analyzed (analysis region) and boundary conditions. FIG. 10 is a diagram showing analysis conditions other than those shown in FIG. FIG. 11 is a diagram showing an element division state near the face. FIG. 12 is a diagram showing geological conditions. FIG. 13 is an enlarged view of the boundary portion between the natural ground and the support (sprayed concrete). FIG. 14 is a diagram showing an outline of a nuclear fuel cycle. FIG. 15 is a diagram showing a schematic configuration of a geological disposal facility for high-level radioactive waste.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention (hereinafter referred to as “embodiments”) will be described with reference to the accompanying drawings.

  FIG. 1 is a block diagram showing a configuration of a stability evaluation apparatus according to an embodiment of the present invention. The stability evaluation apparatus 1 shown in the figure is an apparatus for evaluating the stability of a natural ground around a mine shaft provided in a geological disposal facility for high-level waste. The stability evaluation apparatus 1 is realized by using an interface such as a keyboard, a mouse, and a touch panel, and includes an input unit 2 that receives input of various information, a calculation unit 3 that executes various calculations related to stability evaluation of natural ground, and a liquid crystal Alternatively, an output unit 4 that is realized by using a display panel made of organic EL or the like and displays and outputs various types of information including the stability evaluation result, and various types of information including information such as parameters necessary for the calculation unit 3 to execute the calculation. A storage unit 5 that stores information and a control unit 6 that controls the operation of the stability evaluation apparatus 1 are provided.

  The computing unit 3 compares a nonlinear strain measure calculated by the numerical analysis unit 31 with a predetermined allowable value, and a numerical analysis unit 31 that calculates a nonlinear strain measure that is an evaluation index of stability by performing a numerical analysis related to excavation. As a result of comparison between the comparison unit 32 and the comparison unit 32, when the nonlinear strain measure is equal to or less than the allowable value, the displacement calculation unit 33 that calculates the wall displacement corresponding to the nonlinear strain measure, and the wall displacement calculated by the displacement calculation unit 33 And an evaluation unit 34 that evaluates the stability of the natural ground by comparing the wall displacement of the mine measured with actual excavation.

  The storage unit 5 includes a design condition storage unit 51 that stores the design conditions input by the input unit 2, and a model information storage unit 52 that stores information related to a numerical analysis model executed when evaluating the stability. Have.

  Design conditions stored by the design condition storage unit 51 include geological conditions, installation conditions, tunnel shape and dimensions, and support settings. Among these, geological conditions are elastic modulus, Poisson's ratio, internal friction angle, adhesive strength, uniaxial compressive strength, and the like. Further, the installation conditions are excavation depth, initial ground pressure corresponding to the excavation depth, excavation length (excavation section), and the like.

The model for numerical analysis stored in the model information storage unit 52 is a model called a piecewise linear strain softening model. FIG. 2 is a diagram showing an outline of a piecewise linear strain softening model. A curve C _ss shown in FIG. 2 is a stress-strain curve obtained by performing a triaxial compression test using a sample obtained by boring or the like in a natural ground such as soft rock. In FIG. 2, the horizontal axis represents axial strain (ε ₁ ), and the vertical axis represents axial differential stress (σ ₁ −σ ₃ ). The piecewise linear strain softening model uses four axial strains (elastic limit strain ε _e , peak strain ε _p , softening onset strain ε _s , flow onset strain ε _f ) to generate stress-strain curves C _ss in five states I to After dividing into V, it is obtained by approximating with a line segment (straight line) for each state. As shown in FIG. 3, the stress-strain curve changes according to the value of the constraint pressure σ ₃ during the triaxial compression test.

FIG. 4 is a diagram showing the relationship between the elastic limit strain ε _e , the peak strain ε _p , the softening start strain ε _s , the flow start strain ε _f, and the constraint pressure σ ₃ . Further, FIG. 5, the value of the ratio of elastic limit strain epsilon value of the ratio of the peak strain epsilon _p for _{e ε p / ε e = η} p, elastic limit strain softening starting strain for _{ε e ε s ε s / ε} e = It is a figure which shows the relationship between (eta) _s and the value (epsilon) _f / (epsilon) _e = (eta) _f of restraint pressure (sigma) _3, and ratio ratio of the flow start strain _| epsilon (epsilon) _{f with} respect to elastic limit strain (epsilon) _e . These ratio values η _p , η _s , η _f are called state strain ratios. The state strain ratios η _p , η _s , and η _f are obtained by using the uniaxial compressive strength σ _c ,
^{_{η p = 2σ c -0.18, η}} s = 3σ c -0.25, η f = 5σ c -0.32
(Aidan Omer, Tomoyuki Akagi, Kamimoto Kawamoto, “Parameters (state strain) as criteria for squeezing level”, 25th Symposium on Rock Mechanics, Japan Society of Civil Engineers (89)) , Pp. 426-430, 1993).

FIG. 6 shows the relationship between the axial differential stress σ ₁ −σ ₃ and the axial strain ε ₁ and the volume strain ε _V and the axial strain ε ₁ in the piecewise linear strain softening model obtained by the triaxial compression test of the natural ground material. It is a figure which shows a relationship. In FIG. 6, the broken line OABCD indicates the relationship between the axial differential stress σ ₁ -σ ₃ and the axial strain ε ₁ , and the broken line OA′B′C′D ′ indicates the relationship between the volume strain ε _V and the axial strain ε _1. Is shown. Note that f, g, and h in the figure indicate volume increase rates in the sections A′B ′, B′C ′, and C′D ′, respectively (hereinafter referred to as gradients f, g, and h).

  The stability evaluation apparatus 1 having the above functional configuration is realized using a computer including a CPU having calculation and control functions. The CPU included in the stability evaluation device 1 can be variously read out from the storage unit 5 by reading various programs including information stored and stored in the storage unit 5 and a program for executing the stability evaluation method according to the present embodiment. Perform arithmetic processing.

  FIG. 7 is a flowchart showing an outline of processing of the stability evaluation method according to the present embodiment. When evaluating the stability of natural ground, design is performed by setting various conditions (step S1). The conditions set in step S1 are input by the input unit 2 of the stability evaluation apparatus 1 and stored in the design condition storage unit 51.

  A specific example of setting conditions will be shown below. FIG. 8 is a diagram showing an example of setting the cross-sectional shape and dimensions of the tunnel of the geological disposal facility in soft rock. In the present embodiment, for example, a mine having a circular cross section with an inner diameter of 5 m and an excavation diameter of 6 m is set as an analysis target. If such a tunnel is used, an axisymmetric analysis can be performed and a model by sequential excavation can be simplified. For the support, for example, only sprayed concrete is considered, and the thickness of spraying is 0.5 m.

  FIG. 9 is a diagram schematically illustrating a setting example of a region to be analyzed (analysis region) and boundary conditions. In the case shown in FIG. 9, the analysis area is 100 (m) × 100 (m). The final face position is 60 m from the boundary so as not to be affected by the boundary.

  FIG. 10 is a diagram showing analysis conditions other than those described above. In the case shown in FIG. 10, the installation depth is set to 500 m, the initial ground pressure is set to 10.79 MPa, and the excavation length is set to 0.5 m. In addition, the cycle time when the construction plan of the geological disposal facility is set to 2 days a week with 5 days of operation is the excavation time of 135 minutes, the time required for shotcrete (including invert) is 70 minutes, rock bolt + other processing Is set to 35 minutes.

  FIG. 11 is a diagram illustrating an element division state in the vicinity of a face in a tunnel. The natural ground and shotcrete are divided into 0.1 m x 0.25 m as elements near the face. Thereby, the natural ground excavation part is subdivided into areas a ′ and b ′, and the shotcrete is subdivided into areas a and b. In addition, the area | region n of FIG. 11 has shown the face excavation area. Moreover, area | region i, i-1, ... has shown the area where shotcrete was installed in the distance of L1 from the face.

  FIG. 12 is a diagram showing geological conditions. As the geological condition, for example, an SR-D rock grade ground is used as a soft rock grade. As physical properties of this rock-grade natural ground, elastic modulus, Poisson's ratio, internal friction angle, adhesive force, uniaxial compressive strength, converted uniaxial compressive strength, and state strain are set. In addition, it is also possible to use a natural ground having a bedrock grade of SR-E.

Among the geological conditions shown in FIG. 12, the converted uniaxial compressive strength is a strength calculated from the adhesive force and the internal friction angle using the Mohr-Coulomb yield condition. Specifically, the Mohr-Coulomb yield conditions in the section AB having the peak intensity at the polygonal line OABCD in FIG. 6 are axial pressure (maximum principal stress) σ ₁ , constraint pressure (minimum principal stress) σ _{3 at} the peak intensity, and By using the reduced uniaxial compressive strength σ _c ,
σ ₁ −κσ ₃ −σ _c = 0 (1)
It is expressed. Here, the converted uniaxial compressive strength σ _c and the constant κ are expressed by the following equations (2) and (3), respectively, using the adhesive strength c _p and the internal friction angle φ _p at the peak strength.

Also, the Mohr-Coulomb yield conditions in the section CD of the residual strength in the polygonal line OABCD in FIG. 6 are the axial pressure (maximum principal stress) σ ′ ₁ of the residual strength, the constraint pressure (minimum principal stress) σ ′ ₃ , and the conversion uniaxial By using the compressive strength σ ' _c
σ ′ ₁ −κ′σ ′ ₃ −σ ′ _c = 0 (4)
It is expressed. Here, in terms of the uniaxial compressive strength sigma _'c and the constant kappa', using the adhesive force c _r and the internal friction angle phi _r in residual strength, the following equations (5), represented by (6).

  Next, a piecewise linear strain softening model is formed from a stress-strain curve obtained by conducting a triaxial compression test of the natural ground material (step S2). Information about the formed piecewise linear strain softening model is stored in the model information storage unit 52. It is also possible for the stability evaluation apparatus 1 to automatically generate a piecewise linear strain softening model from the stress-strain curve information by the calculation unit 3.

を算出する。ここで、式（７）の右辺のｅ^p _ij（ｉ，ｊ＝ｘ，ｙ，ｚ）は偏差塑性ひずみであり、塑性ひずみε^p _ijおよびクロネッカーのデルタδ_ijを用いることにより、

で定義される（ｉ，ｊ，ｋ＝ｘ，ｙ，ｚ）。なお、本実施の形態において、同じ項に含まれるテンソルの共通の添え字については和をとるものとする。 Thereafter, the numerical analysis unit 31 performs numerical analysis of excavation of the natural ground in the mine part based on the design conditions stored in the design condition storage unit 51 (step S3). Specifically, the piecewise linear strain softening model is incorporated into the strain softening model in the finite difference method code FLAC (see, for example, Itasca Consulting Group, Inc., “FLAC User's Guide”, 2000.) to perform analysis. At this time, the numerical analysis unit 31 uses a nonlinear strain measure as a stability evaluation index.

Is calculated. Here, e ^p _ij (i, j = x, y, z) on the right side of Equation (7) is a deviation plastic strain, and by using the plastic strain ε ^p _ij and the Kronecker delta δ _ij ,

(I, j, k = x, y, z). In the present embodiment, the common subscripts of tensors included in the same term are summed.

を用いることにより、

と表される。また、係数α_gは、勾配ｇを用いて定義されるダイレイタンシー角

を用いることにより、

と表される。 Between the main plastic strains ε ^p ₁ and ε ^p ₃ ,
ε ^p ₃ = −α _f・ ε ^p ₁ , ε ^p ₁ = −α _g・ ε ^p ₃
There is a relationship. Where the coefficient α _f is the dilatency angle defined using the gradient f

By using

It is expressed. The coefficient α _g is a dilatancy angle defined using the gradient g.

By using

It is expressed.

と表される。ここで、弾性限界ひずみε^e ₁は、地山の弾性係数Ｅ、拘束圧σ₃および換算一軸圧縮強度ε₀を用いて、

と表される。
このように、区分線形ひずみ軟化モデルにおいて、弾性限界ひずみε^e ₁より大きい軸ひずみに対応する非線形ひずみ測度は、弾性限界ひずみε^e ₁を基準として与えられる。 Subsequently, the comparison unit 32 compares the magnitude relationship between the calculated nonlinear strain measure ε ^(p) and a predetermined allowable value ε ^(p) _per (step S4). This allowable value ε ^(p) _per can be arbitrarily set as long as it is a nonlinear strain measure corresponding to an axial strain having a magnitude equal to or larger than the elastic limit strain ε ^e ₁ in the piecewise linear strain softening model. For example, if the natural ground follows the Mohr-Coulomb yield criterion, an allowable value using one of the nonlinear strain measures ε ^(p) _s , ε ^(p) _f corresponding to the axial strains ε ^s ₁ , ε ^f ₁ , respectively. ε ^(p) _per can be defined. Here, the nonlinear strain measures ε ^(p) _s and ε ^(p) _f are respectively expressed by using equations (7) to (12).

It is expressed. Here, the elastic limit strain ε ^e ₁ is obtained by using the elastic coefficient E of the natural ground, the restraint pressure σ ₃ and the converted uniaxial compressive strength ε ₀ .

It is expressed.
Thus, in piecewise linear strain softening model, nonlinear distortion measure corresponding to the elastic limit strain epsilon ^e ₁ strain larger axis is given the elastic limit strain epsilon ^e ₁ as a reference.

In the interval linear strain softening model formed in step S2, for example, it is assumed that the strength constant φ at the time of strain softening is equal to the internal friction angle φ _p at the peak strength (φ = φ _p ). adhesion c, nonlinear distortion measure epsilon ^(p), using ^{_{ε (p) s, ε (}} p) f, adhesion c _r during adhesion c _p and the residual strength of the peak intensity, the following equation (16 ) To (18).

As a result of comparison by the comparison unit 32, when ε ^(p) ≦ ε ^(p) _per (step S4: Yes), it can be evaluated that the natural ground is stable. In this case, in order to evaluate the stability after actual excavation, the displacement calculation unit 33 calculates the wall surface displacement U of the tunnel that generates the nonlinear strain measure ε ^(p) (step S5). On the other hand, if the comparison unit 32 compares ε ^(p) > ε ^(p) _per (step S4: No), the ground is unstable, so the process returns to step S1 to review the design conditions. Is done.

を算出する。その後、変位算出部３３は、一つの掘進長ａ〜ｂ内の壁面変位Ｕ_avの平均値

を算出し、掘進区間における壁面変位とする。ここで、式（１９）の右辺のＵ_av ^a、Ｕ_av ^bは、それぞれ領域ａ、ｂにおける節点変位の平均値である。 FIG. 13 is an enlarged view of the boundary portion between the natural ground and the support (sprayed concrete). Displacement calculating unit 33 first natural ground element G of the nodal displacements at the boundary between the支保element T U _j, as U j _{+ 1,} nodal displacements U _j, the average value of U j _{+ 1}

Is calculated. Thereafter, the displacement calculation unit 33 calculates the average value of the wall surface displacement U _av within one digging length ab.

Is calculated as the wall displacement in the excavation section. Here, U _av ^a, U _av ^b of the right side of the equation (19) is the average value of the nodal displacements in the region a, b, respectively.

  After step S5, excavation is actually performed (step S6). The excavation at this time is performed for a predetermined excavation length according to the construction plan described above.

  After that, the wall surface displacement u in a predetermined excavation length of the mine shaft generated by excavation is measured (step S7). The measurement here may be performed according to a known method.

  Subsequently, the evaluation unit 34 evaluates the stability of the natural ground by comparing the displacement amount U obtained by numerical analysis and the displacement amount u obtained by measurement (step S8). As a result of comparison by the evaluation unit 34, when u ≦ U is satisfied (step S8: Yes), the evaluation unit 34 evaluates that the natural ground around the excavated mine shaft is stable (step S9). In this case, when excavation is continued (step S10: Yes), the process returns to step S6. On the other hand, when excavation is not continued (step S10: No), a series of processing ends.

  On the other hand, as a result of the comparison by the evaluation unit 34, if u> U (step S8: No), the evaluation unit 34 evaluates that the natural ground around the excavated mine shaft is unstable (step S11). ). In this case, when the process is continued (step S12: Yes), the process returns to step S1 to reset the design conditions. On the other hand, when the process is not continued (step S12: No), the series of processes is terminated.

  According to the embodiment of the present invention described above, the stress-strain curve obtained from the triaxial compression test of the natural ground material is expressed in terms of the axial strain value, assuming that the natural ground conforms to the Mohr-Coulomb yield criterion. A nonlinear strain measure calculated by forming a piecewise linear strain softening model that segments and linearizes, and performing numerical analysis of excavation of ground in the tunnel based on this model, and a nonlinear strain corresponding to a predetermined axial strain In order to evaluate the stability of natural ground by comparing with the tolerance value that is a measure, it is possible to maintain high evaluation accuracy even when it is applied even when it has a tunnel shape other than circular or when complex excavation is performed. It becomes possible.

  Moreover, according to this Embodiment, since the nonlinear distortion measure is used as a stability evaluation index, the stability of the natural ground can be quantitatively evaluated.

  Further, according to the present embodiment, when the nonlinear strain measure obtained by numerical analysis is less than the allowable value, the wall displacement corresponding to the nonlinear strain measure is calculated, while the actual excavation is performed according to the set conditions. In order to measure the wall displacement of the excavated mine after the excavation, and to evaluate the stability of the excavated natural ground based on the calculated wall displacement and the measured wall displacement, high precision stability while proceeding with construction Can be evaluated.

  In addition, according to the present embodiment, the axial strain that determines the allowable value has a value equal to or greater than the softening start strain in the piecewise linear strain softening model, and thus cannot be used in the technique described in Patent Document 1. An allowable value can be set, and a more accurate evaluation of stability can be performed.

DESCRIPTION OF SYMBOLS 1 Stability evaluation apparatus 2 Input part 3 Calculation part 4 Output part 5 Storage part 6 Control part 31 Numerical analysis part 32 Comparison part 33 Displacement calculation part 34 Evaluation part 51 Design condition storage part 52 Model information storage part

Claims (6)

A stability evaluation method for evaluating the stability of natural ground around a tunnel,
A design process for setting conditions including the geological conditions of the natural ground and the installation conditions of the tunnel,
A piecewise linear strain softening model in which the ground is in accordance with the Mohr-Coulomb yield criterion, and the stress-strain curve obtained from the triaxial compression test of the groundstone material is sectioned and linearized by the value of the axial strain. A model forming process for forming a piecewise linear strain softening model in which the stress changes linearly when the strain increases from the softening onset strain to the flow onset strain ;
A numerical analysis step for calculating a nonlinear strain measure in a predetermined excavation section by performing a numerical analysis of excavation of a natural ground in a mine part based on a piecewise linear strain softening model formed in the model formation step;
A comparison step of evaluating the stability of the natural ground by comparing the nonlinear strain measure calculated in the numerical analysis step with an allowable value which is a nonlinear strain measure corresponding to a predetermined axial strain in the piecewise linear strain softening model. When,
The stability evaluation method characterized by having. As a result of comparison in the comparison step, when the nonlinear strain measure calculated in the numerical analysis step is less than or equal to the allowable value, a displacement calculation step of calculating a wall displacement corresponding to the nonlinear strain measure;
Excavation process for excavation according to the conditions set in the design process;
A measuring step of measuring wall displacement of the tunnel excavated in the excavation step;
An evaluation step for evaluating the stability of the excavated ground based on the wall displacement calculated in the displacement calculation step and the wall displacement measured in the measurement step;
The stability evaluation method according to claim 1, further comprising:   The stability evaluation method according to claim 1, wherein the predetermined axial strain has a value equal to or greater than an elastic limit strain in the piecewise linear strain softening model. A stability evaluation device for evaluating the stability of natural ground around a tunnel,
The stress-strain curve obtained from the triaxial compression test of the natural ground material is assumed to be in accordance with the conditions including the geological condition of the natural ground and the conditions for installing the tunnel, and the natural ground according to the Mohr-Coulomb yield criterion. A piecewise linear strain softening model formed by sectioning and linearizing with the value of, where the stress changes linearly when the strain increases from the softening start strain to the flow start strain. A storage unit for storing;
A numerical analysis unit that calculates a nonlinear strain measure in a predetermined excavation section by performing numerical analysis of excavation of a natural ground based on a piecewise linear strain softening model stored in the storage unit;
A comparison unit that evaluates the stability of the natural ground by comparing the nonlinear strain measure calculated by the numerical analysis unit and an allowable value that is a nonlinear strain measure corresponding to a predetermined axial strain;
A stability evaluation apparatus comprising: As a result of the comparison by the comparison unit, when the nonlinear strain measure calculated by the numerical analysis unit is equal to or less than the allowable value, a displacement calculation unit that calculates a wall displacement corresponding to the nonlinear strain measure;
An evaluation unit that evaluates the stability of the excavated natural ground based on the wall displacement calculated by the displacement calculating unit and the wall displacement measured in the tunnel excavated according to the conditions;
The stability evaluation apparatus according to claim 4, further comprising:   The stability evaluation apparatus according to claim 4, wherein the predetermined axial strain has a value equal to or greater than a softening start strain in the piecewise linear strain softening model.

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